1. Technical Field of the Invention
The present invention relates to a driving unit used to reduce rotation speed of a hydraulic motor and output the reduced rotation speed, which is used as a driving device for a traveling apparatus.
2. Description of the Prior Art
A driving unit is used as a driving device of a construction machine traveled by a crawler as typified particularly by a driving device of a hydraulic shovel among construction machines. In the driving unit, a hydraulic motor is disposed in an interior of a fixed casing fixed to a vehicle body, so that the rotation as output is transmitted to a rotating casing concentrically fitted to the fixed casing to freely rotate through a planetary gear mechanism, so as to drive the crawler by means of a sprocket disposed around a periphery of the rotating casing. Because of the constraint that the driving unit is located in the interior of the crawler, there is a restriction on the entire inner configuration space, for the reason of which the driving unit is required to have small size and high power.
The driving units of this type are known by publications such as Japanese Laid-open (Unexamined) Patent Publications No. Hei 4-140538, No. Hei 6-249297, Hei 8-247223 and No. Hei 9-240525.
However, the driving units of this conventional type are all being demanded to be further downsized.
It is the object of the present invention to provide a driving unit structurally optimized for every principal part, to provide downsizing and improved durability.
In accordance with a 1st aspect of the invention, there is provided a driving unit comprising a fixed casing having a hydraulic motor therein; a rotating casing rotatably supported around a periphery of the fixed casing via a bearing inserted from one end portion of the fixed casing and having an internal gear around an inside thereof; a sun gear mounted on an output shaft projected from the hydraulic motor toward the one end portion of the fixed casing; a planetary gear train disposed between the sun gear and the internal gear to reduce speed in two or more stages; a trunnion boss, integrally projected from the one end portion of the fixed casing, for rotatably supporting the planetary gear train of a final stage engaging with the internal gear; a holder in which a front end portion of the trunnion boss is inserted; support pillars projecting from the holder toward the fixed casing; and fastening means for fixing the support pillars and the fixed casing.
Known as a conventional driving unit is the one disclosed by Japanese Laid-open (Unexamined) Patent Publication No. Hei 4(1992)-140538, for example. A typical conventional driving unit 101 is shown in FIG. 25. The driving unit 101 has a cylindrical fixed casing 102 in which a hydraulic motor 103 is disposed. An output shaft 104a of the hydraulic motor 103 is coupled with an input shaft 104b via a spline coupling 117, and a sun gear 105 is mounted on a front end portion of the input shaft 104b. A rotating casing 107 is rotatably supported around a periphery of the fixed casing 102 via a bearing 106, and an internal gear 108 is formed around an inside of the rotating casing 107. The rotation of the sun gear 105 is transmitted to the internal gear 108 through a planetary gear 109, a second sun gear 111 engaged with a planetary gear frame 110 of the planetary gear 109, and a second planetary gear 113 supported on a trunnion boss 112 projected from the front end portion of the fixed casing 102, to rotate the rotating casing 107 at a reduced speed. A flange 114 of the fixed casing 102 is bolted to the body (not shown), and a flange 115 of the rotating casing 107 is bolted to a crawler sprocket (not shown).
The driving torque of the hydraulic motor 103 fixedly mounted in the fixed casing 102 is reduced via a planetary gear train of the first stage comprising the sun gear 105 and the planetary gears 109 and a planetary gear train of the second stage comprising a second sun gear 111 and second planetary gears 113 and is transmitted to the rotation of the rotating casing 107.
However, since the trunnion boss 112 for rotatably supporting the second planetary gears 113 is projected from the end of the fixed casing 102 in a cantilever fashion, a bending stress is generated at the basal end of the trunnion boss 112 when a load is applied thereto through the second planetary gears 113. For this reason, the trunnion boss 112 is required to have a large thickness. As a result of this, the bearing 106 and the floating seal 116 inserted from the trunnion boss 116 side of the fixed casing 102 are increased in size, which causes the rotating casing 107 to increase in size and in turn causes the entire driving unit 101 to increase in radial dimension.
According to the construction of the 1st aspect of the invention, the trunnion boss is allowed to be supported at opposite ends thereof by the holder fixed to the fixed casing through the support pillars. This enables the load applied to the trunnion boss to be dispersed to the holder and the fixed casing, and as such can allow the trannion boss to be reduced in diameter or can allow the fixed casing to be reduced in circumferential dimension. This produces the result that the rotating casing supported around the periphery of the fixed casing by the bearing inserted thereon is also reduced in outer diameter. Also, the support pillars projected from the holder have thickness such that even when the holder body is small in thickness, the fastening means to be fixed to the fixed casing applies a sufficient fastening force at the support pillars. This enables the support of the planetary gear train for rotation, without any axial elongation and with good durability. Thus, the downsizing of the driving unit can be achieved and improved durability can also be provided.
In accordance with a 2nd aspect of the invention, there is provided a driving unit according to 1st aspect of the invention, wherein the support pillars are in abutment with support pillars projected from the fixed casing at their abutment surfaces, which are located within a width of the planetary gear of the final stage.
This construction enables the abutment surfaces to be away from the basal ends of the support pillars to which a maximum bending moment is applied, by projecting the support pillars from the fixed casing side as well.
In accordance with a 3rd aspect of the invention, there is provided a driving unit according to 1st aspect of the invention, wherein the trunnion boss is projected along a periphery of the fixed casing and a rounded portion is formed at a basal end of the trunnion boss except an area close to the periphery of the fixed casing.
According to this construction, since the direction of the load acting on the trunnion boss is a tangent direction to the fixed casing, the fixed casing can be reduced in circumferential diameter by forming no rounded portion for relaxing the bending stress at the basal end of the trunnion boss located around the periphery of the fixed casing.
In accordance with a 4th aspect of the invention, there is provided a driving unit according to 1st aspect of the invention, wherein the abutment surfaces are located at an approximately widthwise center portion of the planetary gear of the final stage.
This construction can allow the abutment surfaces to be located at an approximately axial center of the support pillar at which a bending moment is minimized. Also, this construction can ensure a dimension from underhead of the bolt used as the fastening means to the abutment surfaces.
In accordance with a 5th aspect of the invention, there is provided a driving unit comprising a fixed casing having a hydraulic motor therein; a rotating casing rotatably supported around a periphery of the fixed casing via a bearing inserted from one end portion of the fixed casing and having an internal gear around an inside thereof; a sun gear mounted on an output shaft projected from the hydraulic motor toward the one end portion of the fixed casing; a planetary gear train disposed between the sun gear and the internal gear to reduce speed in two or more stages; a trunnion boss, supported at the one end portion of the fixed casing, for rotatably supporting the planetary gear train of a final stage engaging with the internal gear; a holder in which a front end portion of the trunnion boss is inserted; support pillars projecting from the holder toward the fixed casing; and fastening means for fastening the support pillars and the fixed casing, wherein the support pillars are in abutment with support pillars projected from the fixed casing at their abutment surfaces, which are located within a width of the planetary gear of the final stage.
According to this construction, the trunnion boss is allowed to be supported at opposite ends thereof by the fixed casing and the holder fixed to the fixed casing through the support pillars. This enables the load applied to the trunnion boss to be dispersed to the holder and the fixed casing, and as such can allow the trannion boss to be reduced in diameter or can allow the fixed casing to be reduced in circumferential dimension. This produces the result that the rotating casing supported around the periphery of the fixed casing by the bearing inserted thereon is also reduced in outer diameter. Also, since the abutment surfaces at which the support pillars projected from the holder and the support pillars projected from the fixed casing are in abutment are within the width of the planetary gear of the final stage, the support pillars projected from the holder have thickness such that even when the holder body is small in thickness, the fastening means to be fixed to the fixed casing applies a sufficient fastening force at the support pillars. This enables the support of the planetary gear train for rotation, without any axial elongation and with good durability. Also, by projecting the support pillars from the fixed casing side as well, the abutment surfaces can be allowed to be away from the basal ends of the support pillars to which a maximum bending moment is applied. Thus, the downsizing and improved durability of the driving unit can be achieved.
In accordance with a 6th aspect of the invention, there is provided a driving unit according to 5th aspect of the invention, wherein the abutment surfaces are located at an approximately widthwise center portion of the planetary gear of the final stage.
This construction can allow the abutment surfaces to be located at an approximately axial center of the support pillar at which a bending stress is minimized. Also, this construction can ensure a dimension from underhead of the bolt used as the fastening means to the abutment surfaces.
In accordance with a 7th aspect of the invention, there is provided a driving unit comprising a hydraulic motor and a planetary gear type of reducer to reduce an output of the hydraulic motor and transmit the reduced output to a driving portion, wherein an output shaft portion of the hydraulic motor and an input shaft portion of the reducer are integrally formed in the form of a single rotating shaft; wherein a sun gear of the reducer is put in spline engagement with a front end portion of the rotating shaft; and wherein the spline is so formed that a clearance therebetween can gradually broaden toward the end thereof
With the conventional type of driving unit 101, since the output shaft 104a and the input shaft 104b are coupled with the coupling 117 using the spline engagement, the driving unit is increased in radial dimension as well as in axial length at that coupling part.
In contrast to this, with the construction of the 7th aspect of the invention, since the rotating shaft can be used both as the input shaft and as the output shaft by projecting the output shaft of the hydraulic motor beyond the center of the reducer, no intermediate coupling is required, thus enabling the radial thickness of the rotating shaft to be optimized. The rotating shaft is journaled by two bearings in the hydraulic motor at two lengthwise locations thereof. When pressure is introduced into the cylinder block, the rotating shaft is subject to a bending load at its portion between the two bearings, so that the front end portion of the rotating shaft is inclined. However, since the spline cogs of the rotating shaft are formed in a crowning fashion or a like fashion so that it can gradually narrow toward the front end to produce a clearance gradually broadened toward the front end, so as to ensure the clearance corresponding to the inclination of the rotating shaft. This can allow the rotating shaft to surface-contact with the sun gear to transmit the running torque of the rotating shaft to the sun gear smoothly.
In accordance with a 8th aspect of the invention, there is provided a driving unit according to 7th aspect of the invention, wherein spline grooves are formed around an inside of the sun gear so that they are each located at an approximately circumferential center between adjacent spaces between cogs formed around a periphery of the sun gear.
According to this construction, since the spaces between the cogs of the sun gear and the spline grooves at the fitting portions between the sun gear and the rotating shaft are out of position from each other with respect to the circumferential direction, even when the sun gear is reduced in diameter, the wall thickness of the sun gear can be ensured.
In accordance with a 9th aspect of the invention, there is provided a driving unit comprising a hydraulic motor and a planetary gear type of reducer to reduce an output of the hydraulic motor and transmit the reduced output to a driving portion, wherein an output shaft portion of the hydraulic motor and an input shaft portion of the reducer are integrally formed in the form of a single rotating shaft; wherein a sun gear of the reducer is mounted on a front end portion of the rotating shaft; and wherein at least one of a planetary gear engaging with the sun gear and the sun gear have cogs which are so formed that a clearance therebetween can gradually broaden toward the end thereof.
According to this construction, since the rotating shaft can be used both as the input shaft and as the output shaft by projecting the output shaft of the hydraulic motor beyond the center of the reducer, no intermediate coupling is required, thus enabling the radial thickness of the rotating shaft to be optimized. Also, the sun gear and/or the planetary gears allow for the clearance corresponding to the inclination of the rotating shaft, so that the surface-contact between these gears is ensured.
In accordance with a 10th aspect of the invention, there is provided a driving unit according to 8th aspect of the invention, wherein a distance between P and a tangent line touching one tooth flank of the sun gear at a point and extending perpendicularly to an axis of the sun gear is set at a value of not less than and asymptotic to 2 "igr" sin xcex8 when the reducer is in an unloaded state:
where xcex4 is a maximum radial variation of the sun gear caused by inclination of the rotating shaft; xcex8 is an angle formed by the tangent line and a moving direction of the sun gear in such a positional relationship that when the rotation shaft is inclined, the one tooth flank of the sun gear which is on the opposite side to the other tooth flank of the sun gear which is put into engagement with the planetary gear comes nearest to a confronting tooth flake of the planetary gear; and P is a point on the tooth flank of the planetary gear closest to the sun gear.
According to this construction, even when the rotating shaft is inclined, the sun gear and the planetary gears can be prevented from colliding with each other at a tooth flake on the opposite side to a tooth flake at which they are engaged with each other.
In accordance with a 11th aspect of the invention, there is provided a driving unit comprising a hydraulic motor and a planetary gear type of reducer to reduce an output of the hydraulic motor and transmit the reduced output to a driving portion, the driving unit comprising a sun gear coupled with an output shaft portion of the hydraulic motor, planetary gears engaging with the sun gear, and an internal gear engaging with the planetary gears and formed around an inside of a rotating casing of the reducer, wherein a length of pass of contact of the internal gear is shortened so that an engaging area between the planetary gears and the sun gear can be equal in durable period to that between the internal gear and the sun gear.
This construction can allow the internal gear to reduce in length, and as such can allow the rotating casing to be reduced in size. Thus, the internal gear and the casing can be reduced in weight and further the costs for hardening treatment of the internal gear can be cut.
In accordance with a 12th aspect of the invention, there is provided a driving unit comprising a fixed casing having a hydraulic motor therein; a rotating casing rotatably supported around a periphery of the fixed casing via a bearing inserted from one end portion of the fixed casing and having an internal gear around an inside thereof; a sun gear mounted on an output shaft projected from the hydraulic motor toward the one end portion of the fixed casing; and a planetary gear train disposed between the sun gear and the internal gear to reduce speed, wherein at least one stage of the planetary gear train has two planetary gears symmetrically disposed about the output shaft and a planetary gear frame for rotatably supporting the two planetary gears at both axial ends thereof in sandwich relation, the planetary gear frame having a pair of flat plate portions for supporting the two planetary gears in sandwich relation and support pillars for connecting between the pair of flat plate portions, the support pillars being partially extended along a periphery of the flat plate portions and disposed near the planetary gears.
In general, the driving unit having three planetary gears arranged in regular triangle, as disclosed by Japanese Laid-open (Unexamined) Patent Publication No. Hei 8(1996)-247223, for example, is in wise use, in term of the stable support configuration. At present, it can be said that it has reached a critical limit for the structure having the three planetary gears to further reduce parts count and downsizing of the components.
The construction according to the 12th aspect of the invention can produce the driving unit with two planetary gears having a structural stability. Hence, as compared with the conventional type of driving unit having three planetary gears, parts count can be reduced to a large extent and also the structure can be simplified. Hence, the driving unit having an advantage in cost can be produced.
In accordance with a 13th aspect of the invention, there is provided a driving unit according to 12th aspect of the invention, wherein the flat plate portions are formed into a generally ellipse-like shape.
This construction enables the components of the driving unit comprising the two planetary gears to be further reduced in size and weight by forming the planetary gear frame into an ellipse-like shape.
In accordance with a 14th aspect of the invention, there is provided a driving unit comprising a fixed casing having a hydraulic motor therein; a rotating casing rotatably supported around a periphery of the fixed casing via a bearing inserted from one end portion of the fixed casing and having an internal gear around an inside thereof; a sun gear mounted on an output shaft projected from the hydraulic motor toward the one end portion of the fixed casing; a planetary gear train disposed between the sun gear and the internal gear to reduce speed in two or more stages; a trunnion boss, disposed at the one end portion of the fixed casing, for rotatably supporting the planetary gear train of a final stage engaging with the internal gear; a holder in which a front end portion of the trunnion boss is inserted and which is mounted on the fixed casing; a nut threadedly engaged with the periphery of the fixed casing to position the bearing with respect to an axial direction of the fixed casing; and a key plate for locking the nut against rotation, wherein the key plate is fixed at a position corresponding to an end face of the fixed casing from which the trunnion boss is projected.
In the driving unit, the bearing for rotatably supporting the rotating casing around the periphery of the fixed casing is generally positioned by the nut, to which a lock means is given. Known as this type of conventional driving unit is the one disclosed by Japanese Laid-open (Unexamined) Patent Publication No. Hei 6(1994)-249297, which is shown in FIG. 26. The driving unit 118 has a cylindrical fixed casing 119 in which a hydraulic motor 120 is disposed. A first sun gear 122 is mounted on a front end portion of an output shaft 121 of the hydraulic motor 120. A rotating casing 124 is rotatably supported around a periphery of the fixed casing 119 via a bearing 123, and an internal gear 125 is formed around an inside of the rotating casing 124. The rotation of the first sun gear 122 is transmitted to the internal gear 125 through a first planetary gear 126, a second sun gear 128 engaged with a planetary gear frame 127 of the first planetary gear 126, a third sun gear 130 engaged with the planetary gear flame 129 of the second planetary gear 128, and a third planetary gear 132 rotatably supported on a carrier 131 threadedly engaged with the fixed casing 119, to rotate the rotating casing 124 at a reduced speed. A flange 133 of the fixed casing 119 is bolted to the body (not shown), and a flange 134 of the rotating casing 124 is bolted to a crawler sprocket 135.
The rotating casing 124 is rotatably supported to the fixed casing 119 via the bearing 123, for which a conical roller bearing is used, and a preload is applied to the bearing 123 by screwing the nut 136 with an adequate torque. In order to keep the bearing 123 in the state in which the preload is applied thereto, the nut 136 must be locked against rotation. For this reason, the structure shown in FIGS. 27(a), 27(b) is adopted, wherein a key plate 137 having a key 137a to be fitted in a key slot 119a of the fixed casing 119 and the nut 136 are fixed by bolts 138. A number of threaded holes 136a are formed in the side of the nut 136 at regular intervals so that the bolts 138 can be screwed in the related threaded holes 136a by only a slight turning of the nut 136 which is in an adequate fastened state.
However, due to the structure that the key slot 119a is formed in the fixed casing 119 and, in addition to the nut 136, the key plate 137 and bolt heads 138 are interposed between the bearing 123 and the carrier 131, a distance d between the nut 136 and the end portion of the fixed casing 119 is disadvantageously elongated.
With the construction according to the 14th aspect of the invention, since the planetary gear of the final stage and the key plate are so disposed as to be partially overlapped, the driving unit can be reduced in axial dimension to the extent corresponding to the overlapped portion.
In accordance with a 15th aspect of the invention, there is provided a driving unit according to 14th aspect of the invention, wherein support pillars projected from the fixed casing and support pillars projected from the holder are fixed in abutment with each other, and the key plate is fixed to the end face of the fixed casing in the state of being partially engaged in a cutout portion of the support pillar on the fixed casing side.
According to this construction, since the key plate is disposed in place by means of the cutout portions provided in the support pillars between the holder for supporting the front end portion of the trunnion boss and the fixed casing, it can be prevented from interfering with the planetary gears.
In accordance with a 16th aspect of the invention, there is provided a driving unit according to 14th aspect of the invention, wherein the trunnion bosses are disposed along the periphery of the fixed casing.
This construction enables the fixed casing to be reduced in circumferential dimension by extending the fixed casing along a circumscribed circle of the trunnion bosses. This enables the driving unit to be reduced in radial dimension as well as in axial dimension.
In accordance with a 17th aspect of the invention, there is provided a driving unit comprising a fixed casing having a hydraulic motor therein; a rotating casing rotatably supported around a periphery of the fixed casing via a bearing inserted from one end portion of the fixed casing and having an internal gear around an inside thereof; a sun gear mounted on an output shaft projected from the hydraulic motor toward the one end portion of the fixed casing; a planetary gear train disposed between the sun gear and the internal gear to reduce speed in two or more stages; a trunnion boss, disposed at the one end portion of the fixed casing, for rotatably supporting the planetary gear train of a final stage engaging with the internal gear; a holder in which a front end portion of the trunnion boss is inserted and which is mounted on the fixed casing; and a nut threadedly engaged with the periphery of the fixed casing to position the bearing with respect to an axial direction of the fixed casing; and a pin, disposed between the nut and the holder, for locking the nut against rotation.
According to this construction, since the nut and the holder are connected by the pin without any use of the key plate, the nut can be locked against rotation without any elongation of the axial dimension of the fixed casing.
In accordance with a 18th aspect of the invention, there is provided a driving unit according to 17th aspect of the invention, wherein support pillars projected from the fixed casing and support pillars projected from the holder are fixed in abutment with each other, a projection projecting from the holder along a periphery of the support pillar, and the pin is disposed between the projection and the nut.
According to this construction, at the same time when the holder is inserted toward the fixed casing so that the end faces of the support pillars at the front ends thereof are put into abutment with each other, the nut is locked against rotation by means of the pin.